1. Field of the Invention
This invention relates to a control system for hybrid vehicles having an internal combustion engine and a traction motor as prime movers.
2. Prior Art
Conventionally, a hybrid vehicle having an internal combustion engine (hereinafter simply referred to as "the engine") and a traction motor as prime movers is widely known, and a control system for controlling the prime movers of such a hybrid vehicle has already been proposed e.g. by Japanese Patent Laid-Open Patent Publication (Kokai) No. 5-229351.
The proposed control system determines the optimum torque at which the maximum engine efficiency is attained, in dependence on traveling conditions of the vehicle, and at the same time detects actual torque generated by the engine for actually driving the vehicle. Then, the control system determines or selects demanded torque from the optimum torque and the actual torque. When the optimum torque is selected as the demanded or required torque, and at the same time, the optimum torque is larger than the actual torque, regenerative current is caused to be generated for regeneration of energy (specifically, electrical energy).
In the above publication, it is not clearly disclosed whether or not the regeneration of electrical energy is carried out during idling of the engine. If the regeneration of electrical energy is carried out during idling of the engine with load on the engine increased, the combustion efficiency of the engine is enhanced due to the increased load on the engine. However, the increased load on the engine entails an increase in the amount of fuel supplied to the engine, which leads to degraded fuel economy.